1. Field of the Invention
The present invention relates to a control apparatus of an internal combustion engine for controlling the supply of evaporated fuel gas and exhaust gas downstream from a throttle valve of an intake pipe.
2. Description of the Related Art
In an internal combustion engine, a process known as “evaporated fuel purge” is performed to temporarily store an evaporated fuel gas occurring in a fuel tank in a canister, and, by supplying the stored evaporated fuel gas into an intake pipe, thereby combusting the evaporated fuel gas in a combustion chamber. A process known as EGR for refluxing an exhaust gas flowing through an exhaust pipe into the intake pipe is also performed. Related art which performs the evaporated fuel purge and EGR is disclosed in Japanese Patent Laid-Open Publication No. Hei 10-115258. As described in that publication, the EGR rate and the purge rate are suppressed and the region where the purge rate becomes constant is enlarged while the evaporation concentration exceeds a set value and, when the evaporation concentration reduces to the set value or less and has less influence as disturbance, the purge rate and the EGR rate are increased. Thereby, enhancement in fuel economy and reduction in exhaust emission by the EGR are carried out while securing the evaporated fuel purge ability.
In other related art, control of a throttle opening degree of an internal combustion engine is disclosed in Japanese Patent Laid-Open Publication No. Hei 9-250376, Japanese Patent Laid-Open Publication No. Hei 10-213015 and Japanese Patent Laid-Open Publication No. Hei 8-317507.
In the aforementioned art, the purge rate and the EGR rate are both increased when the evaporation concentration reduces to the set value or less. However, the pressure of the exhaust gas is higher than that of the evaporated fuel gas, and, therefore, the exhaust gas flows into the intake pipe more easily than the evaporated fuel gas. Accordingly, it is difficult to sufficiently increase the purge amount with respect to the increase in the EGR amount, thus creating the problem that a desired purge amount cannot be reliably or easily secured.